Why do credit cards have expiration dates, and other questions you were afraid to ask

If you’re an American adult, there’s a good chance you have lived decades of your life alongside a small, silent object that holds many secrets. That object? Your credit card.

As it turns out, these cards have a lot going on that you have probably never thought could be explained...until now. Every detail of this little item has a purpose, and now it’s time to find out what they are.

Why do credit and debit cards have expiration dates?

It may seem like banks just want to inconvenience you by having an expiration date on your card, but there are actually several reasons why it’s there. The first, most simple explanation is that cards physically wear out after a period of time. The magnet strip and lamination fall apart after so many years of use, so banks are being proactive in replacing them.

"But some of my credit cards don’t have an expiration date and they’re automatically replaced in the mail," you’re probably saying to yourself.

Well, the secondary reason that most banks change the cards on a regular basis is to prevent fraud. After all, if someone out there is in possession of the numbers to your card, the simplest way to make sure they can’t use it is to have new numbers. So, if you have a card without an expiration date, it's probably one that you got at a store, where they simply don’t care as much about fraud and don’t bother changing the numbers for you.

Do the numbers actually mean anything?

It’s easy to think that the numbers on your card are just a bunch of randomly assigned digits, but believe it or not, those numbers actually mean something.

The first digits determine which company is providing your card. If it starts with a 3, it’s American Express, Carte Blanche, or Diner’s Club. If it has a 4, it’s Visa; 5 is Mastercard, and 6 is Discover. The five digits after that indicate the bank that is issuing the card and what kind of card it is.

The rest of the numbers are more personal, as they indicate the cardholder’s account as well as the "check numbers." The "check numbers" are what the computer looks at quickly to determine if the card is valid or not, but it’s also short enough that if someone had to check manually they could do so.

And this is where your credit card has a little math magic trick up its sleeve: If you want to know whether a card is valid or not, look at the first number (if the card has 16 digits) or the second number (if the card has 15 digits). After that, look at every other number and double them. If the numbers you come up with have two digits, then add those together (so, for example, if you are doubling 6, then you come up with 12, and 1+2 = 3). After you have all of those numbers, add them up with the alternating numbers before they were doubled. If the sum is divisible by ten, then you likely have a valid card.

Why are credit cards the size and shape that they are?

Credit cards are a standard size that is shared with most identification cards such as licenses as well as business cards. While we might take this standardization for granted now (especially when it comes to organizing our wallets) the way this came about is more complex than you might think.

The grandfather of these kinds of cards is the calling card, something that people would use as early as the 15th century in China, but they truly started getting popular during King Louis XIV’s reign in France in the 17th century. People used these cards to announce themselves at a party they wished to attend, and depending on how the people inside felt about their social standing, they were admitted or rejected. These calling cards eventually evolved to be the business cards we carry around with us today.

The original calling cards were a bit bigger than the business and credit cards we have now (they were closer to the size of playing cards) and they eventually became smaller. There are a few different theories for this. Some think that it could have something to do with how many fit side by side on a printing press. Others speculate they’re smaller so that they can fit more easily into a wallet. Still others speculate that since the cards were often held together alongside the owner’s tobacco tin, everyone would prefer the cards be the same size as the tin. Regardless, the result is the convenient standard credit card size that you have today.

So there you have it. The next time you take your debit or credit card out of your wallet to pay for something, you won’t take for granted the secrets that little gadget holds!

Megan is an editor and freelance writer living in Brooklyn, NY. She likes cats, coffee, and reasonably short walks on the beach.

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